Feature request: show current namespace in a status bar

### Describe the issue you are having
Ride is not presenting the current namespace. It would be nice to see the current namespace in a status line.
As a more advanced feature would be to present the list of namespaces to choose from/switch to by clicking on a current namespace in a status bar.

### Did you connect to an already running interpreter or start the interpreter from RIDE?
Start an interpreter

### How do you reproduce the issue?

### Paste the contents of Help → About (Shift+F1)
```
IDE:
Version: 4.1.3151
Platform: Linux x86_64
Date: 2018-04-20 17:00:22 +0200
Git commit: 98cdb1278456012d2cc257831a253b58901a1a1a
Preferences:{
"blinkCursor":"0",
"blockCursor":"1",
"colourScheme":"Francisco Goya",
"cursorBlinking":"solid",
"kbdLocale":"en_US",
"keys":"{\"BK\":[\"Ctrl-Up\"],\"FD\":[\"Ctrl-Down\"],\"LBR\":[\"F10\"],\"LL\":[\"Ctrl-A\",\"Home\"],\"RL\":[\"Ctrl-E\",\"End\"],\"SA\":[],\"TL\":[],\"PF10\":[]}",
"otherExe":"/opt/mdyalog/16.0/64/unicode/mapl",
"selectionHighlight":"1",
"squiggleTips":"1",
"zoom":"5"
}

Interpreter:
Version: 16.0.32456
Platform: Linux-64
Edition: Unicode/64
Date: Mar 13 2018 at 03:31:46

```

No files or tests are named. Start by locating the status-bar UI entry point and the interpreter namespace handling, then determine how the current namespace is obtained. Done means the current namespace is visible in the status line; clickable namespace selection and switching should be clarified before implementation.

Written by the indexing model from the issue text.